There is a heretofore known imaging device applicable to a digital camera, an optical sensor, and so forth, which is constructed by mounting an imaging element e.g. of CCD type or CMOS type on a wiring board. In such an imaging device, for example, an imaging element is mounted on a wiring board, and a lens is disposed above the imaging element by a lens securing member, so that the imaging element and the lens can be sealed by the lens securing member. Moreover, electronic components including a capacitor and a resistor are installed around the imaging element. The imaging device is designed to convert light (image) inputted to a light-receiving section of the imaging element mounted on the wiring board into an electric signal by the imaging element, and output a converted signal to an external circuit or the like within a digital camera via a connecting member such for example as a bonding wire, a wiring conductor of the wiring board, and an external terminal.
In one of known examples of such an imaging device (refer to Patent Literature 1, for example), in the interest of area reduction in the imaging device for miniaturization, a recess is formed at an upper surface of a wiring board, and an imaging element is disposed on the upper surface of the wiring board so as to cover the recess. Moreover, a plurality of electronic components including an IC, a capacitor, a coil, and a resistor for processing electric signals from the imaging element are mounted on the bottom of the recess. In another known example of the imaging device (refer to Patent Literature 2, for example), a recess is formed at a lower surface of a wiring board, and a plurality of electronic components including an IC, a capacitor, a coil, and a resistor for processing electric signals from an imaging element are mounted inside the recess.
A wiring board such as adopted in those imaging devices is made of an insulating material such as ceramics or resin. For example, in the case of using ceramics, the wiring board can be fabricated by laminating a plurality of ceramic green sheets of predetermined configuration on top of each other and then firing the resultant stacked body. In keeping up with the recent trend toward low-profile imaging devices, the recess formed in the wiring board has a bottom thickness in a range of about 0.3 mm to 0.4 mm, and has a depth in a range of about 0.3 mm to 0.4 mm. That is, the constituent ceramic green sheets are very small in thickness.